As for semiconductor wafer inspecting apparatuses, there are two kinds: an inspecting apparatus which inspects a wafer while rotating the wafer and an inspecting method while scanning a wafer in the X and Y directions. A method according to the present invention relates to a method for optically irradiating a wafer with a beam while rotating the wafer and moving the wafer rectilinearly in a radial direction, and detecting a defect on the wafer such as a foreign object by utilizing scattered light reflected on the wafer.
As a method for detecting intensity of scattered light of the wafer, using a signal which is output from an angle detector (encoder) attached to a rotational stage, the detection signal is subject to A/D conversion and subsequent signal processing such as filtering to detect a size and coordinates of a foreign object or a defect.
In a foreign-object/defect inspecting apparatus which inspects a surface by rotating a wafer to scan a beam spirally, an elliptical beam which is oblong in the radial direction as for a shape of the beam to be casted with is used.
In a conventional technique, scattered light of the elliptical shape is detected by a single photodetector (for example, a photomultiplier) to detect a foreign object or a defect on a wafer. There is also an example in which a photodetector of the multi-anode type is used instead of a photomultiplier as a method of scattered light detection; however, it becomes necessary to calibrate the optics system with high accuracy such that it is necessary to align the optical axis of the elliptical beam with the multi-anode direction.
As a conventional example concerning a detecting method using a multi-anode, there is an optical inspecting apparatus described in Patent Literature 1 (JP-A-2005-3447). According to Patent Literature 1, it is described that a multi-anode detector is arranged in a long side direction of a beam of an elliptic shape.